Tube-BOZ

Tyimo

Member
2002-11-16 3:43 pm
Hungary
Hi!

I read in the BOZ article that :
"...I did not find it practical to build a single gain stage tube amplifier, but the relaxed conditions under which a preamp functions makes a tube version of this circuit workable. Simply adjust the voltage and bias values for a tube instead of the MOSFET we will use here...."

Well, could somebody help me how to calculate the voltage and bias values for a Tube-BOZ? I would use E88CC tube with the original 60V PSU, if it is possible. So I could compare the 2 different version, which would give nicer sound, etc.

Thanks!

Tyimo
 

Tyimo

Member
2002-11-16 3:43 pm
Hungary
O.K. Hugo!

Here is your eye candy :)

(The whole article is on the passdiy site, if somebody wouldn't know it.)

Greets:

Tyimo
 

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Although it's tempting to compare the solid state version with a tube version using the same rail voltage, I think you'll find that 60V is a little on the low side for tubes. It will work (I've seen people run tubes on rails as low as 15V), but the comparatively low B+ (you'll probably end up with around 30V at the plate) will give you higher distortion. It could be a really nice-sounding preamp, but it wouldn't be fair to compare it directly to the MOSFET version.
As an engineering exercise or just for fun, I'd say go for it. If you want it to sound better, stretch things out a bit more. Yes, that will require a separate power supply, or possibly a single, more complex one. An ordinary 1:1 isolation transformer is just dandy for a 165V rail. That would be a cheap and easy way to give the tube a higher rail without having to drop a lot of money. Use 1N4007s for the bridge; everybody has a few of those gathering dust. If money is real tight, you could use the caps out of a disposable camera. They're free and good for around 300V, well over the requirements you'd need for this circuit. Then, let's say...oh, I dunno, something like a 100 to 1k resistor to make a CRC filter.
Tinker with it a bit. It'll be fun.

Grey